Ultrasonic imaging in the medical field is widely used for a variety of applications. In addition to imaging physiological structures and tissue such as organs, tumors, vessels, and the like, it is often desirable for a physician or technician to have an image of a medical device which has been inserted into the tissue or passageway of a patient. The types of devices which are surgically sterilized and inserted into patients are many. Typical examples include: needles, catheters and a variety of other medical products such as stents, dilators, pacing leads, introducers, angiography devices, angioplasty devices, pacemakers, in-patient appliances such as pumps and other devices. Various approaches have been used to enhance ultrasonic imaging by modifying the reflective surface characteristics of these devices.
U.S. Pat. No. 4,401,124 to Guess et al. discloses a system for reflection enhancement of a biopsy needle showing grooves cut in the tip of the needle. The reflection coefficient of the needle is enhanced by the use of a defraction grading disposed on the surface of the needle. The defraction grading is formed by the substantially parallel grooves, where the distance between the depth of adjacent grooves is a function of the wavelength of the ultrasound imaging system and the angle of the incident beam with respect to the surface of the needle. The spaced grooves provide constructive interference of the beam, thereby yielding maximum reflection back along the line of the incident beam.
Although the Guess et al. system with its helical defraction grading around the tip of the needle, along with other needles having similar rings, may provide some degree of signal reinforcement along the axis of incident energy, the overall image is far from ideal. Further, needles of this type typically exhibit a marked loss of resolution as the needle is oriented away from an optimum angle relative to the incident ultrasound beam, which angle depends upon the particular ring parameters.
What is needed is a device which provides more accurate monitoring of a surgical instrument such as a needle inserted into the body, which does not require a specific angle of orientation for its efficiency, and which is inexpensive to manufacture.
Another system for enhancing the ultrasound image of a portion of a medical instrument is disclosed in U.S. patent application Ser. No. 194,861, filed May 17, 1988, and owned by the assignee of the present application.
Furthermore, medical devices exist in which radiopaque stripes or additives are utilized to make the medical device appear on an X-ray machine or other radiographic device. For example, U.S. Pat. No. 365,750 to Sheridan et al. discloses an X-ray type catheter having an X-ray opaque pigment on the catheter tube.
One disadvantage of some X-ray opaque medical devices is that there is a risk of the X-ray opaque material flaking or peeling off and remaining in the patient. Furthermore, with these X-ray opaque paints and with the outer surface treatment utilized in the ultrasonic imaging device, fabrication expenses are increased.